Arrangement for inhibiting the unthreading of casing string during well completions

ABSTRACT

A plurality of sections of tubular members is arranged in endto-end relationship with couplings between the sections of tubular members for connecting them together. The sections of tubular members and couplings are provided with left-hand threads to inhibit the unthreading of the tubular sections during well completions. The casing string may include so-called auxiliary equipment for aiding in floating it into position in the well bore and guide equipment which is also provided left-hand threads.

United States Patent 1191 Wilhelm Aug. 21, 1973 [54] ARRANGEMENT FOR INHIBITING THE 1,659,478 2/1928 Black 166/225 UNTHREADING 0 CASING STRING 1,781,091 11/1930 Wilson 3,231,019 l/1966 Clay et a] 166/242 X DURING WELL COMPLETIONS Billy M. Wilhelm, c/o Parker Drlg. Co., Box 3644, Quito, Ecuador Filed: July 7, 1971 Appl. No.: 160,401

Inventor:

References Cited UNITED STATES PATENTS 2/1938 Singleton 285/175 3/1949 McManaway 285/175 X Primary Examiner-David H. Brown Attorney-Jack W. Hayden [5 7] ABSTRACT A plurality of sections of tubular members is arranged in end-to-end relationship with couplings between the sections of tubular members for connecting them together. The sections of tubular members and couplings are provided with left-hand threads to inhibit the unthreading of the tubular sections during well completions. The casing string may include so-called auxiliary equipment for aiding in floating it into position in the well bore and guide equipment which is also provided left-hand threads.

2 Claims, 2 Drawing Figures ARRANGEMENT FOR INHIBITING THE UNTHREADING OF CASING STRING DURING WELL COMPLETIONS BACKGROUND OF THE INVENTION The present invention relates to wells such as oil and gas wells wherein the well bore is provided with a casing incorporating a plurality of sections of tubular members that are adapted to be threadedly engaged by couplings therebetween. At the present time, such tubular sections are provided with right-hand threads as is the auxiliary equipment used in connection with positioning and cementing the casing in place in the well bore. Such auxiliary equipment includes float collars to aid in floating the tubular sections into the well bore and to enable the casing to float and fill with liquid as it is lowered into the well bore section by section. A guide shoe may be provided at the lower end of the casing to inhibit its becoming lodged on a shoulder, projection, dog leg, or other obstruction in the well bore.

After the casing is lowered into the well bore, cement is then pumped down the casing and into the space between the casing and the well bore to secure the casing in position and thereafter the cement is drilled out at the bottom of the casing with a conventional drill string and drill bit on the lower end thereof.

During the drilling of the well bore, undesirable formations, such as water sands, may be encountered and it is necessary to lower casing and cement it in place and then drill out the cement plugs and flotation equipment.

Heretofore, during such operations, the rotation of the drill bit within the casing has in some instances caused the tubular threaded sections of the casing to unthread since the bit is rotating in a direction which tends to cause such action by reason of its frictional engagement with the concrete within the casing string, and since the couplings and tubular sections of the well casing are right-hand threadedly connected together.

SUMMARY OF THE INVENTION The present invention is directed to an arrangement for inhibiting the unthreading of casing and auxiliary equipment connected therewith during drilling out a cement plug in a well such as an oil or gas well.

Another object of the present invention is to provide left-hand threads on the auxiliary equipment such as floating equipment, guiding equipment, and the like used in connection with casing in a well bore to inhibit unthreading thereof during drilling out of the cement in the casing.

Still another object of the present invention is to provide casing with left-hand threads to inhibit unthreading thereof during the right-hand rotation of a drill string with a drill bit internally of the casing.

Yet another object of the present invention is to provide a casing string having certain portions thereof which are connected by right-hand threaded sections and other portions which are connected by left-hand threads to inhibit unthreading of the casing during drilling out of the concrete within the casing.

Other objects and advantages of the present invention will become apparent from a consideration of the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view illustrating a well bore with a casing therein formed of tubular sections of members connected by couplings and concrete positioned in the annulus between the casing and well bore walls to position the casing within the well bore. The casing is shown as having a portion thereof with righthand threads and a portion with left-hand threads; and

FIG. 2 is an enlarged view of the lower portion of the casing string shown in FIG. 1 with a combination guide shoe and float collar arrangement on the lower end thereof and illustrating in dotted line a drill string being lowered into position to drill out the portion of the concrete remaining within the lower end of the casing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1 wherein the invention is illustrated generally by the numeral 2, a plurality of sections of tubular members referred to by the numeral 11 is shown as being positioned in end-to-end relationship in the well bore 15, and connected together by the couplings 17a adjacent the ends of each of the tubular members 11. It will be noted that the upper portion of the casing formed by the couplings 17a and tubular members 11 are right-hand threadedly connected together.

The lower portion of the casing formed by tubular members 11 and connecting couplings 17 are shown as being provided with left-hand threads, as shown at 18 for engaging with similar mating left-hand threads 19 internally of the couplings 17 whereby the tubular sections of the casing are connected together. A combination float guide shoe is illustrated generally by the numeral 25 at the lower end of the casing string, and it will be noted that the casing string is shown as being cemented in position in the well bore 15 by the cement 27.

Such cement is positioned in the annulus 26 between the casing string referred to generally by the numeral 9 and the well bore 15 by means well known in the art. It is pumped from the earth's surface (not shown) and internally of the casing string 9 whereupon it is discharged out the opening 41 in the casing and into the annulus 26 and around the casing string to position it in the well bore and to seal off a particular formation such as that illustrated at 35 in FIG. 1 of the drawings.

After the cementing operations have been concluded, there is always a slug of cement left in the lower end of the casing between the cement plug referred to generally by the numeral 40 and the lower end 30 of the float and guide shoe referred to generally at 25. It is desirable to drill out this portion of the cement internally of the casing string 9 as well as the plug 40, and to accomplish this, a drill bit as referred to at 45 in dotted line is lowered into the casing and rotated to the right in a normal manner.

It will be noted that the auxiliary equipment such as the float and guide shoe 25 is connected to the section of tubular member 11 immediately thereabove by lefthand threads 18 on the tubular section 11 and mating left-hand threads 25a internally of the float and guide shoe 25.

Thus, when the drill bit is rotated to the right as viewed in FIG. 2 of the drawings in a normal manner, such rotation will tend to tighten rather than loosen the threads between the tubular sections 1 l which are connected together by the couplings l7, and also this will tend to tighten the connection between the casing and its auxiliary equipment such as the cementing equipment used in positioning the cement within the well bore.

It can be appreciated that separation of the casing string during the drilling operation aforementioned can be quite costly, and in some instances, causes the loss of a well.

The present invention would overcome this problem in that the provision of the left-hand thread on the tubular sections forming the casing as well as on the couplings connecting the ends of the tubular members together and the auxiliary equipment used in connection with the casing provides an arrangement which prevents the separation of the casing by right-hand rotation of the drill string.

In some instances, it may be desirable to provide three or four sections of tubular members immediately above the cementing equipment at the lower end of the casing with left-hand threads and then the remainder, if desired, could be provided with normal right-hand threads. As shown in FIG. 1, the lower portion of the casing string is formed by tubular members and couplings having left-hand threads, while the upper portion near the earths surface has right-hand threads.

When the casing and the shoe and flotation are provided with right-hand threads, the weight on the drill bit is maintained at a level to try to inhibit the casing sections from unthreading. For example, under such conditions, the weight on the drill bit may be maintained in the range of 8,000 to 15,000 pounds. When this procedure is followed, it may take from one to three hours or longer to drill out the cement plugs and floating equipment.

However, with the present invention, wherein lefthand threads are employed, much more weight could be applied during the drilling operations to expedite drilling of the plug and flotation equipment.

Also, the left-hand thread arrangement of the present invention would eliminate the time-consuming operation of putting thread locking compound on each casing section. This procedure presently employed on right-hand threads requires that all foreign matter be removed from the threads and then putting on the thread locking compound. Such procedure also requires backing off, or unthreading a casing collar on each joint of casing so that the compound may be put on the threads and then the coupling is rethreaded on the casing section.

In some instances, the shoe and floating equipment and the collars connecting the casing sections are spot welded on one end to the casing sections, but even this, in some instances, does not prevent the casing from unthreading.

Of course, where a plurality ofcasings is employed, this invention may be employed on each string.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, and materials as well as in the details of the illustrated construction may be made without departing from the "spirit of the invention.

What is claimed is:

, 1. An arrangement for inhibiting the unthreading of casing string including:

a. a plurality sections section of tubular members in end-to-end relationship to form a casing string for a well; l.

b. coupling means for engaging the ends of adjacent tubular members together; and g c. said sections and coupling means each having lefthand threads for engaging the couplings and sections together to maintain said sections in end-toend relationship.

2. The invention of claim 1 wherein the casing string incorporates a float collar and a guide shoe for guiding the casing string into the well andwherein the guide shoe is connected to the casing string with left-hand threads.

UNITED STATES PATENT OFFICE ERTIFICATE 0F CORRECTION August 21, 1973 Patent No. 464 Dated Inventor(s) Billy Wi elm It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4, Line 27 "a plurality sections sect-ion" should be -a plurality of sections Signed and sealedfthis 25th day of December 19-73.

(SEAL) Attest; v

EDWARD M.FLETGHER,JR. RENE D. TEGTMEYEE Attesting Officer Acting Commissioner of Patents FORM PO-IOSO 0-69) 

1. An arrangement for inhibiting the unthreading of casing string including: a. a plurality sections section of tubular members in end-to-end relationship to form a casing string for a well; b. coupling means for engaging the ends of adjacent tubular members together; and c. said sections and coupling means each having left-hand threads for engaging the couplings and sections together to maintain said sections in end-to-end relationship.
 2. The invention of claim 1 wherein the casing string incorporates a float collar and a guide shoe for guiding the casing string into the well and wherein the guide shoe is connected to the casing string with left-hand threads. 